A lithographic system applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic system can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive compound (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.
Being able to guarantee defect-free imaging in extreme ultraviolet light (EUV) lithographic systems may be necessary for a successful introduction and acceptance in the market of EUV lithographic systems. Particles on the patterning device are one of the main sources of imaging defects, because the EUV patterning device is not covered by a membrane or pellicle (as is common for deep ultraviolet light (DUV) patterning devices) which keeps any contamination out of focus. For the next generation lithography tools, particles with a diameter of 30 nm and larger may be detrimental. Inspecting the patterning device before moving the patterning device to an exposure position is a desired aspect of a patterning device handling process for extreme ultraviolet patterning devices.